[fsp] Do not allow write operations on read only file systems.

chrome/browser/chromeos/file_system_provider/operations/open_file.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/file_system_provider/operations/open_file.h"
 
 #include <string>
 
 #include "chrome/common/extensions/api/file_system_provider.h"
 #include "chrome/common/extensions/api/file_system_provider_internal.h"
@@ skipping 11 matching lines @@
     : Operation(event_router, file_system_info),
       file_path_(file_path),
       mode_(mode),
       callback_(callback) {
 }
 
 OpenFile::~OpenFile() {
 }
 
 bool OpenFile::Execute(int request_id) {
+  if (!file_system_info_.writable() &&
+      mode_ == ProvidedFileSystemInterface::OPEN_FILE_MODE_WRITE) {
+    return false;
+  }
+
   scoped_ptr<base::DictionaryValue> values(new base::DictionaryValue);
   values->SetString("filePath", file_path_.AsUTF8Unsafe());
 
   switch (mode_) {
     case ProvidedFileSystemInterface::OPEN_FILE_MODE_READ:
       values->SetString(
           "mode",
           extensions::api::file_system_provider::ToString(
               extensions::api::file_system_provider::OPEN_FILE_MODE_READ));
       break;
@@ skipping 20 matching lines @@
 
 void OpenFile::OnError(int /* request_id */,
                        scoped_ptr<RequestValue> /* result */,
                        base::File::Error error) {
   callback_.Run(0 /* file_handle */, error);
 }
 
 }  // namespace operations
 }  // namespace file_system_provider
 }  // namespace chromeos